The invention relates to an apparatus for the fastening of a sensor element to a deformable member, such as, a vehicle axle, in order to monitor the axle deflection as an indication of the load condition of the vehicle.
Such an apparatus is known from the publication of the VDO Vertriebsgesellschaft mbH, Bad Soden, "Loading Weight Scale, Axle-Load Scale", particularly page 11. It describes how a sensor support of a deformation sensor, calibrated as a transmitter for axle loads, is fastened to a second component, such as, an axle housing, by means of one cap screw each at the screw-down points.
On the known apparatus, the screw heads of the cap screws are in direct contact during the tightening and, thereafter, with the screw-down points of the sensor support. As a result of the friction forces produced during the tightening of the cap screws at the screw-down points of the sensor support by the screw heads, the torqrue on the screw heads is transferred to the sensor support, which is essentially deformed in an "S"-shape. The deformation sensor detects this deformation as a background deformation and delivers a corresponding background electrical signal.
If the apparatus has been improperly installed or assembled, this background signal can occupy a significant portion of the operating range of the deformation sensor, so that its remaining operating range for the detection of the actual operational deformations is either insufficient or the sensor signals suffer a decline in precision. As a result of settling phenomena (specifically under the influence of dynamic load changes), there can be a reformation of the background deformation, which can result in a change in the background signal, and thus imprecise measurements or increased measurement imprecision.
On the apparatus described, the deformation sensor is positively connected with the second component (axle housing) to monitor its deformation, as an indication of the load condition. This connection can be distorted by the above-mentioned dynamic load changes, which can result in additional measurement imprecision.
It is conceivable that the disadvantages of the apparatus, described above, could be overcome to, welding the sensor support with the second component. The residual stresses caused by the welding, however, also cause a background signal, which can, if the appratus has been improperly installed or assembled, occupy an unacceptable large portion of the operating range of the deformation sensor. Another disadvantage is that the residual stresses decrease over time, especially with dynamic load changes, which can lead to imprecise measurements or increased measurement imprecision. The welding may also cause problems when a safety-related part, such as, an axle housing, is involved, on account of the residual stresses. Finally, the welding has the further disadvantage that replacing the deformation sensor is time consuming and difficult.
A first component, in the form of a sensor, can also be connected (in the manner described above) with two second components, whose displacements, in relation to one another, it monitors. In this case, too, the above-mentioned disadvantages caused by the attachment apparatus can be expected.
In other cases, e. g., with a tool-holder as the first component and a machine tool bed as the second component, it is necessary for the mutual position of the components to be permanently fixed, even under the action of dynamic influences. This problem, too, cannot be overcome with an apparatus of the type described above.